100G Effort Eyes One Optical Lane

SAN JOSE, Calif. — Engineers will gather here at a two-day workshop starting June 12 in search of a low-cost way for data centers to send 100 Gbit/s over a single optical channel. Their work could spark proposals for high-bandwidth links, specifically a low-cost approach for the 400G Ethernet standards group officially kicked off in May.

Today's communications use bundles of serial copper and optical interconnects, each one delivering data typically at 10 Gbit/s and 25 Gbit/s. Paving a path to 100G over a single optical wavelength or lambda would open the door to much faster individual links and lower-cost links that use parallel bundles.

For example, today's 100G links use ten 10G channels. Engineers expect the first 400GE products to use sixteen 25G channels, but that's not very cost effective.

"Each channel adds another point of cost with more lasers and detectors" in the case of optical links, said John D'Ambrosia, who chairs the IEEE 400GE effort and sparked the idea for the June 100G workshop at an Ethernet trade group meeting last fall. "I asked whether 100G over a single lambda was possible, and no one disagreed. But the technical issues needed to be worked, and no one assumes this will be easy."

So far, the meeting has attracted engineers from Broadcom, Cisco Systems, Dell, Finisar, Fujitsu, JDSU, and other companies, with some attendees planning to come from as far away as Taiwan. They will not write a specification, but they may provide guidance on how to get to one.

"I hope to leave with an industry action plan," said D'Ambrosia, who also led the IEEE 40/100G Ethernet. "The logical path to me is a 4x100G specification for 400GE and then going back to 100G serial optical spec, as well."

Telecom operators already have a high-end spec for 100G over the optical transport network. It uses a relatively exotic modulation scheme and aims at covering many kilometers.

The June workshop is focused on a two-kilometer reach for cost-sensitive data centers such as Google and Facebook. The two-day event will explore the technical and business challenges, particularly in the physical layer design.

thank you John for teh invitation...I was invloved in 10 GHz circuits design while back but for years doing something very different so will have to pass...good luck in designing this, amazing challenge! Kris

Perhaps you want to consider coming to the workshop. I am chairing the session on the technical issues related to coming up with a solution. More information can be found on the Ethernet Alliance / OIDA workshop at http://bit.ly/1fNDC8q.

I agree Bert and would even go father...100Gb/s single lane is mission impossible...high-speed IO speeds do not follow Moore's law, I am sorry...there is no way you can design 100 GHz CDR in CMOS, even at 7nm...Kris

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The response below doesn't seem in line with where Ethernet has gone. First, i haven't heard many individuals refer to 10GBASE-LX4 as a success. Next while it is true that 40G was based on an aggregate of 4x10G, i.e. a prior speed, that is not what happened at 100G. While 100GBASE-SR10 used 10G, -SR4, -LR4, and -ER4 are based on 4 lanes of 4x25G. Furthermore, syncronization was solved via lane markers with the IEEE P802.3ba standard.

THe jump to a 100G serial speed at this time is a very significant one. SO while you are partially correct with the mix of serial / parallel speeds, we are somewhat more challenged this time to jump to the next serial speeed.

It's always the same story, Rick. The standard usually starts out with a single serial link, then to support faster speeds, it parallels several of the old serial links. Then a faster single serial is developed because multiple parallel ones become a problem to synchronize. Then speeds go higher still, and this newer serial link is again connected in parallel.

You can see this in optical and copper interconnects. In fact, 10 Gb/s Ethernet allows both single and parallel link options even for fiber optic links (where coarse WDM is used to create the parallel lanes, e.g. 10GBASE-LR compared with 10GBASE-LX4). Happens over and over again.

Single lane beats parallel lanes, but requires faster electronics and, at these speeds, would require exclusive use of single-mode fiber to achieve any range at all.

Thanks for the great write-up. I am very excited for this workshop given the interest expressed at the IEEE P802.3bs Task Force Meeting in May, where an effective lane rate of 100Gb/s clearly had the most interest.

This has the potential to be a defining moment in the development of network technology.